1. Field of the Invention
The present invention relates to a solar cell including a through hole formed on a semiconductor substrate, a solar cell module, and a method of manufacturing such solar cell.
2. Description of the Related Art
Solar cells are expected as a new energy source that can directly convert clean and inexhaustibly supplied sunlight into electricity.
In general, each solar cell can output an energy of several watts. Accordingly, as a power source for a house, a building or the like, it is common to use a solar cell module that includes a plurality of solar cells connected to one another in order to provide enhanced energy output. The plurality of solar cells arranged in arrangement directions is electrically connected to one another by using wiring members.
In recent years, there have been disclosed methods of providing both a positive electrode and a negative electrode on a back surface side of each of the plurality of solar cells in order to facilitate connection of solar cells (see, for example, Japanese Patent Application Publication No. 64-82570, hereinafter referred to as Patent Document 1). Such solar cells respectively include through holes that extend in directions orthogonal to main surfaces of the so semiconductor substrate. Photogenerated carriers collected by an electrode on the light-receiving surface side of the solar cells are guided to the back surface side of the solar cells through a conductor provided in the through hole.
Meanwhile, a solar cell having a HIT (heterojunction with intrinsic thin layer) structure is known as a solar cell having higher photoelectric conversion efficiency than a conventional crystalline solar cell. The HIT solar cell includes a p-type amorphous silicon layer provided on a light-receiving surface of an n-type crystalline silicon substrate and an n-type amorphous silicon layer provided on a back surface of the n-type crystalline silicon substrate. A substantially intrinsic i-type amorphous silicon layer is interposed between the n-type crystalline silicon substrate and the p-type amorphous silicon layer constituting a p-n junction region, and between the n-type crystalline silicon substrate and the n-type amorphous silicon layer constituting a BSF junction region. With this structure, it is possible to improve characteristics of each of the junction interfaces and thereby to obtain a high photoelectric conversion efficiency.
When this structure of the HIT solar cell is employed as the solar cell described in Patent Document 1, following problems are caused.
According to the solar cell disclosed in Patent Document 1, a SIN film is formed inside the through hole in order to suppress re-coupling of the photogenerated carriers on an inner wall surface of the through hole and to insulate the conductor provided inside the through hole from the electrode on the back surface. Such a SiN film is formed in a high-temperature processing at around 400° C. by a thermal CVD method and thereby exerts a passivation effect.
Meanwhile, the entire processing of manufacturing the HIT solar cell is performed at around 200° C. or lower in order to suppress the thermal damage to the semiconductor substrate. A SiN film formed at around 200° C. exerts an insulation characteristic. However, the SIN film formed at around 200° C. does not exert a favorable passivation effect. As a result, re-coupling of the photogenerated carriers on the inner wall surface of the through hole cannot be suppressed sufficiently, and the photoelectric conversion efficiency of the HIT solar cell is thereby degraded.